Use of hormone therapy and risk of breast cancer detected at screening and between mammographic screens

Abstract

Postmenopausal hormone therapy (HT) is associated with increased risk of breast cancer, but in women undergoing breast cancer screening it is not clear whether use of HT is associated with increased risk of breast cancer detected at screening or between screens (interval cancer). Further, it is unclear whether the use of the HTs that have been common in Scandinavia is associated with higher risk of breast cancer than the HTs used in other countries. Our study was based on data from 296,651 women aged 50-69 years, who participated in the Norwegian Breast Cancer Screening Program during 1995Program during -2004. After a mean enrollment time of 3.8 years, 1,512 women were diagnosed with invasive screen detected breast cancer, and 814 with invasive interval breast cancer. Cox regression models were used to estimate hazard ratios (HRs) of breast cancer associated with HT use, after adjusting for confounders. Ever users of HT had a 58% increased risk of breast cancer, compared to never users. The HRs associated with HT use were 1.45 (95% confidence interval (CI) 5 1.29-1.63) for screen detected and 1.89 (95% CI 5 1.61-2.23) for interval cancer. The difference between screen detected and interval cancer was statistically significant (p 5 0.011). The HR of breast cancer increased with duration of HT use, but significantly more so for interval than for screen detected cancer (use of HT for 5 or more years compared to never use; HR 5 2.91, 95% CI 5 2.10-4.04 and HR 5 1.94, 95% CI 5 1.51-2.50, respectively; p 5 0.002). The population attributable fraction of breast cancer due to HT use was 19.8% overall. Ever users of HT tended to develop a cancer of lower grade. No other differences in histological tumor characteristics were observed between ever and never users of HT among screen detected or interval cancers. The estimated risks of either breast cancer overall with HT use are higher in Norway than reported in similar studies from the U.S. HT-use is a stronger risk factor for interval cancer than for screen detected cancer. The increased risk of interval cancer, which may partly be due to decreased sensitivity of mammograms in HT users, remains a challenge in breast cancer screening programs. ' 2006 Wiley-Liss, Inc.

Different types of postmenopausal hormone therapy and mammographic density in Norwegian women

“…21 The higher mammographic density we find for current E 2 plus NETA EPT use compared to never users is in agreement with the more pronounced risk of breast cancer among HT users in the Norwegian when compared to the US population. 1,2,4,5,22 Although the differences in our study may seem small, the 7% absolute difference in mammographic density between never use and current EPT use for 5 or more years translate to a 100% relative difference.…”

Incidence and tumor characteristics of breast cancer diagnosed before and after implementation of a population-based screening-program

“…First, women not invited or not exposed contribute greatly to the proportion of advanced tumors (Table I). Second, screened women in Norway have been frequent ever users of hormonal therapy, which is known to increase the risk of invasive tumors [11,12]. Furthermore, the introduction of sentinel node diagnostics concurrent with the implementation of the screening program may have increased the detection of positive nodes, because sentinel node technique increases the sensitivity of detecting metastases of breast cancer [13].…”

Endogenous sex hormones, prolactin and mammographic density in postmenopausal Norwegian women

“…30 The reader of the mammograms was experienced and blinded to the characteristics of the women. Furthermore, the hormone analyses were done in a blinded manner at a laboratory specialized on hormone measurements.…”